Ion implanter and electrostatic quadrupole lens device

ABSTRACT

An ion implanter includes a high energy multistage linear acceleration unit for accelerating an ion beam. The high energy multistage linear acceleration unit includes high frequency accelerators in a plurality of stages provided along a beamline through which the ion beam travels, and electrostatic quadrupole lens devices in a plurality of stages provided along the beamline. The electrostatic quadrupole lens device in each of the stages includes a plurality of lens electrodes facing each other in a radial direction perpendicular to an axial direction, and disposed at an interval in a circumferential direction, an upstream side cover electrode covering a beamline upstream side of the plurality of lens electrodes and including a beam incident port, and a downstream side cover electrode covering a beamline downstream side of the plurality of lens electrodes and including a beam exiting port.

RELATED APPLICATIONS

The content of Japanese Patent Application No. 2021-032815, on the basisof which priority benefits are claimed in an accompanying applicationdata sheet, is in its entirety incorporated herein by reference.

BACKGROUND Technical Field

Certain embodiments of the present invention relate to an ion implanterand an electrostatic quadrupole lens device.

Description of Related Art

In a semiconductor manufacturing process, a process of implanting ionsinto a semiconductor wafer (also referred to as an ion implantationprocess) is generally performed in order to change conductivity of asemiconductor, or in order to change a crystal structure of thesemiconductor. A device used for the ion implantation process is calledan ion implanter. Implantation energy of the ions is determineddepending on a desired implantation depth of the ions implanted near asurface of the wafer. A high energy (for example, 1 MeV or higher) ionbeam is used for implantation into a relatively deep region.

In the ion implanter capable of outputting the high energy ion beam, theion beam is accelerated by using a multistage high frequency linearacceleration unit (LINAC). For example, the high frequency linearacceleration unit includes high frequency accelerators in a plurality ofstages for accelerating the ion beam and electrostatic quadrupole lenselectrodes in a plurality of stages for converging the ion beam.

SUMMARY

According to an embodiment of the present invention, there is providedan ion implanter including a high energy multistage linear accelerationunit for accelerating an ion beam. The high energy multistage linearacceleration unit includes high frequency accelerators in a plurality ofstages provided along a beamline through which the ion beam travels, andelectrostatic quadrupole lens devices in a plurality of stages providedalong the beamline. The electrostatic quadrupole lens device in each ofthe stages includes a plurality of lens electrodes facing each other ina radial direction perpendicular to an axial direction in which thebeamline extends while the beamline is interposed between the pluralityof lens electrodes facing each other, and disposed at an interval in acircumferential direction perpendicular to both the axial direction andthe radial direction, an upstream side cover electrode covering abeamline upstream side of the plurality of lens electrodes, andincluding a beam incident port opening in the axial direction, and adownstream side cover electrode covering a beamline downstream side ofthe plurality of lens electrodes, and including a beam exiting portopening in the axial direction. At least one of the upstream side coverelectrode and the downstream side cover electrode which are included inthe electrostatic quadrupole lens device in at least one of theplurality of stages includes at least one gas exhaust port opening inthe radial direction.

According to another embodiment of the present invention, there isprovided an electrostatic quadrupole lens device. The electrostaticquadrupole lens device includes a plurality of lens electrodes facingeach other in a radial direction perpendicular to an axial direction inwhich a beamline extends while the beamline is interposed between theplurality of lens electrodes facing each other, and disposed at aninterval in a circumferential direction perpendicular to both the axialdirection and the radial direction, an upstream side cover electrodecovering a beamline upstream side of the plurality of lens electrodes,and including a beam incident port opening in the axial direction, and adownstream side cover electrode covering a beamline downstream side ofthe plurality of lens electrodes, and including a beam exiting portopening in the axial direction. At least one of the upstream side coverelectrode and the downstream side cover electrode includes at least onegas exhaust port opening in the radial direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view illustrating a schematic configuration of an ionimplanter according to an embodiment of the present invention.

FIGS. 2A to 2C are sectional views illustrating a schematicconfiguration of a linear acceleration unit.

FIGS. 3A and 3B are front views illustrating schematic configurations ofan electrostatic quadrupole lens devices.

FIG. 4 is a sectional view illustrating a schematic configuration of ahigh frequency accelerator.

FIG. 5 is a sectional view illustrating details of a configuration ofthe linear acceleration unit according to an embodiment of the presentinvention.

FIG. 6 is a sectional view illustrating a disposition of a vacuumchamber according to the embodiment of the present invention.

FIG. 7 is an external perspective view illustrating an example of a lensunit when viewed from an upstream side.

FIG. 8 is an external perspective view illustrating the lens unit inFIG. 7 when viewed from a downstream side.

FIG. 9 is a sectional view taken along a beamline, which illustrates adetailed internal configuration of the lens unit in FIG. 7.

FIG. 10 is a sectional view perpendicular to the beamline, whichillustrates a detailed internal configuration of the lens unit in FIG.7.

DETAILED DESCRIPTION

Recently, an ultra-high energy (for example, 4 MeV or higher) ion beamis required for implantation into a deeper region. In order to generatethe ultra-high energy ion beam, it is necessary to further increaseacceleration voltages applied to the high frequency accelerators and tofurther increase focusing/defocusing voltages applied to lenselectrodes. When the voltages applied to the lens electrodes increase,discharge is likely to occur between the electrodes. In particular, whenthe ion beam collides with an electrode body of the lens electrode, theelectrode body is sputtered, and a sputtered substance adheres to andcontaminates the electrode body or an insulating member supporting theelectrode body, the discharge is more likely to occur. In addition,multiply charged ions may be used to generate the ultra-high energy ionbeam. When a degree of vacuum in a beamline decreases, the multiplycharged ions interact with gas remaining in the beamline, and a chargestate of the multiply charged ion tends to be lowered.

It is desirable to provide a technique for suppressing dirt adhering toan electrode body included in an electrostatic quadrupole lens device oran insulating member supporting the electrode body, and improving adegree of vacuum of a beamline.

Any desired combination of the above-described components, and those inwhich the components or expressions according to the present inventionare substituted from each other in methods, devices, or systems areeffectively applicable as an aspect of the present invention.

According to an aspect of the present invention, it is possible tosuppress dirt adhering to the electrode body included in theelectrostatic quadrupole lens device or the insulating member supportingthe electrode body, and to improve the degree of vacuum of the beamline.

Hereinafter, embodiments according to the present invention will bedescribed in detail with reference to the drawings. In describing thedrawings, the same reference numerals will be assigned to the sameelements, and repeated description will appropriately be omitted.Configurations described below are merely examples, and do not limit thescope of the present invention in any way.

Before the embodiments are described in detail, an outline will bedescribed. The present embodiment relates to an ion implanter for highenergy ion beam. The ion implanter causes a high frequency linearacceleration unit to accelerate an ion beam generated by an ion source,transports a high energy ion beam obtained by the acceleration to aworkpiece (for example, a substrate or a wafer) along a beamline, andimplants ions into the workpiece. In the following description, in orderto facilitate understanding, an example will be described on the premisethat the “workpiece (for example, the substrate or the wafer)” is the“wafer”. However, the ion implantation method and the ion implanteraccording to the present disclosure is not limited to the example. Forexample, a specific example of the “workpiece (for example, thesubstrate or the wafer)” includes not only a semiconductor wafer butalso a flat panel display substrate (for example, a glass substrate).

The term “high energy” in the present embodiment means beam energy of 1MeV or higher, 4 MeV or higher, or 10 MeV or higher. According to highenergy ion implantation, desired dopant ions are implanted into a wafersurface with relatively high energy. Therefore, the desired dopant ionscan be implanted into a deeper region (for example, a depth of 5 μm orlarger) of the wafer surface. For example, an application field of thehigh energy ion implantation is to form a P-type region and/or an N-typeregion in manufacturing a semiconductor device such as astate-of-the-art used image sensor.

The high frequency linear acceleration unit includes high frequencyaccelerators in a plurality of stages for accelerating the ion beam andelectrostatic quadrupole lens devices in a plurality of stages forfocusing/defocusing the ion beam. The electrostatic quadrupole lensdevice includes a plurality of lens electrodes facing each other whilethe beamline is interposed between the plurality of lens electrodesfacing each other, an upstream side cover electrode covering a beamlineupstream side of the plurality of lens electrodes, and a downstream sidecover electrode covering a beamline downstream side of the plurality oflens electrodes. Each of the upstream side cover electrode and thedownstream side cover electrode has a beam passage port through whichthe ion beam passes, and functions as a ground electrode.

In order to generate a higher energy ion beam, it is necessary tofurther increase the acceleration voltages applied to the high frequencyaccelerators and to further increase the focusing/defocusing voltagesapplied to the lens electrode. When the voltages applied to the lenselectrodes increase, discharge is likely to occur between the lenselectrode and the cover electrode. The electrode body of the lenselectrode or the cover electrode is disposed close to the beamline.Accordingly, the electrode body is sputtered due to collision of the ionbeam. When the sputtered substance adheres to the electrode body or theinsulating member supporting the electrode body, and the electrode bodyor the insulating member supporting the electrode body is contaminated,discharge is more likely to occur between the electrode bodies. Inaddition, in a space between the upstream side cover electrode and thedownstream side cover electrode of each of the electrostatic quadrupolelens devices, sputtered substance is likely to stay, and the space hasan environment where the electrode body or the insulating membersupporting the electrode body is likely to be contaminated.

In the present embodiment, a gas exhaust port is provided in the coverelectrode of the electrostatic quadrupole lens device. In this manner,the sputtered substance can be easily exhausted outward of the coverelectrode through the gas exhaust port. In addition, since the gasexhaust port is provided, a degree of vacuum in the space between theupstream side cover electrode and the downstream side cover electrode ofeach of the electrostatic quadrupole lens devices, that is, a degree ofvacuum of the beamline of the high frequency linear acceleration unit isincreased. The multiply charged ions may be used to generate the higherenergy ion beam, in some cases. When the multiply charged ions interactwith gas remaining in the beamline, the multiply charged ions have aproperty in which a charge state decreases. In particular, as the chargestate of the multiply charged ions increases, the multiply charged ionstend to interact with residual gas. According to the present embodiment,the gas exhaust port is provided in the cover electrode. In this manner,the residual gas in the beamline can be decreased, and it is possible tosuppress a decrease in a beam current which is caused by a decrease inthe multiply charged ions.

FIG. 1 is a top view schematically illustrating an ion implanter 100according to an embodiment. The ion implanter 100 includes a beamgeneration unit 12, a beam acceleration unit 14, a beam deflection unit16, a beam transport unit 18, and a substrate transferring/processingunit 20.

The beam generation unit 12 has an ion source 10 and a mass analyzer 11.In the beam generation unit 12, the ion beam is extracted from the ionsource 10, and the extracted ion beam is subjected to mass analysis bythe mass analyzer 11. The mass analyzer 11 has a mass analyzing magnet11 a and a mass resolving slit 11 b. The mass resolving slit 11 b isdisposed on a downstream side of the mass analyzing magnet 11 a. As aresult of the mass analysis performed by the mass analyzer 11, only anion species required for implantation is selected, and the ion beam ofthe selected ion species is guided to the subsequent beam accelerationunit 14.

The beam acceleration unit 14 has a plurality of linear accelerationunits 22 a, 22 b, and 22 c for accelerating the ion beam and a beammeasurement unit 23, and forms a linearly extending portion of abeamline BL. Each of the plurality of linear acceleration units 22 a to22 c includes one or more high frequency accelerators respectively inone or more stages, and causes a radio frequency (RF) electric field toact on and to accelerate the ion beam. The beam measurement unit 23 isprovided most downstream of the beam acceleration unit 14, and measuresat least one beam characteristic of the high energy ion beam acceleratedby the plurality of linear acceleration units 22 a to 22 c. The beammeasurement unit 23 measures beam energy, a beam current, a beamprofile, or the like as the beam characteristic of the ion beam. In thepresent specification, the beam acceleration unit 14 is also referred toas a “high energy multistage linear acceleration unit”.

In the present embodiment, three linear acceleration units 22 a to 22 care provided. The first linear acceleration unit 22 a is provided in anupper stage of the beam acceleration unit 14, and includes the highfrequency accelerators respectively in a plurality of stages (forexample, 5 to 15 stages). The first linear acceleration unit 22 aperforms “bunching” of a continuous beam (DC beam) output from the beamgeneration unit 12 to match a specific acceleration phase, andaccelerates the ion beam to have the energy of approximately 1 MeV, forexample. The second linear acceleration unit 22 b is provided in amiddle stage of the beam acceleration unit 14, and includes the highfrequency accelerators respectively in a plurality of stages (forexample, 5 to 15 stages). The second linear acceleration unit 22 baccelerates the ion beam output from the first linear acceleration unit22 a to have the energy of approximately 2 to 3 MeV, for example. Thethird linear acceleration unit 22 c is provided in the lower stage ofthe beam acceleration unit 14, and includes the high frequencyaccelerators respectively in a plurality of stages (for example, 5 to 15stages). The third linear acceleration unit 22 c accelerates the ionbeam output from the second linear acceleration unit 22 b to have thehigh energy of 4 MeV or higher, for example.

The high energy ion beam output from the beam acceleration unit 14 hasan energy distribution in a certain range. Therefore, in order that thehigh energy ion beam is scanned and parallelized downstream of the beamacceleration unit 14 to irradiate the wafer, highly accurate energyanalysis, energy distribution control, trajectory correction, and beamconvergence/divergence adjustment need to be performed in advance.

The beam deflection unit 16 performs energy analysis, energydistribution control, and trajectory correction of the high energy ionbeam output from the beam acceleration unit 14. The beam deflection unit16 forms a portion extending in an arc shape in the beamline BL. Adirection of the high energy ion beam is changed toward the beamtransport unit 18 by the beam deflection unit 16.

The beam deflection unit 16 includes an energy analysis electromagnet24, a horizontally focusing quadrupole lens 26 that suppresses energydistribution, an energy resolving slit 27, a first Faraday cup 28, adeflection electromagnet 30 that provides beam steering (trajectorycorrection), and a second Faraday cup 31. The energy analysiselectromagnet 24 is referred to as an energy filter electromagnet (EFM).In addition, a device group including the energy analysis electromagnet24, the horizontally focusing quadrupole lens 26, the energy resolvingslit 27, and the first Faraday cup 28 is collectively referred to as an“energy analysis device”.

The energy resolving slit 27 may be configured so that a slit width isvariable to adjust resolution of the energy analysis. For example, theenergy resolving slit 27 may be configured to include two blockingbodies that are movable in a slit width direction, and may be configuredso that the slit width is adjustable by changing an interval between thetwo blocking bodies. The energy resolving slit 27 may be configured sothat the slit width is variable by selecting any one of a plurality ofslits having different slit widths.

The first Faraday cup 28 is disposed immediately after the energyresolving slit 27, and is used in measuring the beam current for theenergy analysis. The second Faraday cup 31 is disposed immediately afterthe deflection electromagnet 30, and is provided to measure the beamcurrent of the ion beam which enters the beam transport unit 18 after abeam trajectory correction. Each of the first Faraday cup 28 and thesecond Faraday cup 31 is configured to be movable into and out of thebeamline BL by an operation of a Faraday cup drive unit (notillustrated).

The beam transport unit 18 forms the other linearly extending portion ofthe beamline BL, and is parallel to the beam acceleration unit 14 whilea maintenance area MA in the center of the ion implanter 100 isinterposed therebetween. A length of the beam transport unit 18 isdesigned to be approximately the same as a length of the beamacceleration unit 14. As a result, the beamline BL including the beamacceleration unit 14, the beam deflection unit 16, and the beamtransport unit 18 forms a U-shaped layout as a whole.

The beam transport unit 18 includes a beam shaper 32, a beam scanner 34,a beam dump 35, a beam parallelizer 36, a final energy filter 38, andleft and right Faraday cups 39L and 39R.

The beam shaper 32 includes a focusing/defocusing lens such as aquadrupole lens device (Q lens), and is configured to shape the ion beamhaving passed through the beam deflection unit 16 into a desiredcross-sectional shape. For example, the beam shaper 32 is configured toinclude an electric field type three-stage quadrupole lens (alsoreferred to as a triplet Q lens), and has three electrostatic quadrupolelens devices. The beam shaper 32 can independently adjust convergence ordivergence of the ion beam in each of a horizontal direction(x-direction) and a vertical direction (y-direction) by using the threelens devices. The beam shaper 32 may include a magnetic field type lensdevice, or may include both an electric field and a magnetic field typelens device.

The beam scanner 34 is a beam deflection device configured to providereciprocating scanning with the beam and to perform scanning in thex-direction with the shaped ion beam. The beam scanner 34 has a scanningelectrode pair facing in a beam scanning direction (x-direction). Thescanning electrode pair is connected to variable voltage power supplies(not illustrated), and a voltage applied between the scanning electrodepair is periodically changed. In this manner, an electric fieldgenerated between the electrodes is changed so that the ion beam isdeflected at various angles. As a result, the scanning with the ion beamis performed over a scanning range indicated by an arrow X. In FIG. 1, aplurality of trajectories of the ion beam in the scanning range areindicated by fine solid lines. The beam scanner 34 may be replaced withanother beam scan unit, and the beam scan unit may be configured toserve as an electromagnet device using the magnetic field.

The beam scanner 34 deflects the beam beyond the scanning rangeindicated by the arrow X. In this manner, the ion beam is incident intothe beam dump 35 provided at a position away from the beamline BL. Thebeam scanner 34 causes the ion beam to temporarily retreat from thebeamline BL toward the beam dump 35, thereby blocking the ion beam sothat the ion beam does not reach the substrate transferring/processingunit 20 located downstream of the beamline BL.

The beam parallelizer 36 is configured so that the traveling directionof the ion beam used for the scanning is parallel to a trajectory of thedesigned beamline BL. The beam parallelizer 36 has a plurality ofarc-shaped parallelizing lens electrodes in a central portion of each ofwhich a passing slit for the ion beam is provided. The parallelizinglens electrodes are connected to high-voltage power supplies (notillustrated), and apply the electric field generated by voltageapplication to the ion beam so that the traveling directions of the ionbeam are parallelized. The beam parallelizer 36 may be replaced withanother beam parallelizing device, and the another beam parallelizingdevice may be configured to serve as an electromagnet device using themagnetic field.

The final energy filter 38 is configured to analyze the energy of theion beam and deflect the ions having the required energy downward (inthe −y-direction) so that the ions are guided to the substratetransferring/processing unit 20. The final energy filter 38 is referredto as an angular energy filter (AEF), and has an AEF electrode pair forelectric field deflection. The AEF electrode pair is connected tohigh-voltage power supplies (not illustrated). The ion beam is deflecteddownward by applying a positive voltage to an upper AEF electrode andapplying a negative voltage to a lower AEF electrode. The final energyfilter 38 may be configured to include an electromagnet device formagnetic field deflection, or may be configured to include both the AEFelectrode pair for electric field deflection and the electromagnetdevice for magnetic field deflection.

The left and right Faraday cups 39L and 39R are provided on thedownstream side of the final energy filter 38, and are disposed atpositions into which the left and right end beams in the scanning rangeindicated by the arrow X can be incident. The left and right Faradaycups 39L and 39R are provided at positions that do not block the beamtoward the wafer W, and measure the beam current into the wafer W duringion implantation.

The substrate transferring/processing unit 20 is provided on thedownstream side of the beam transport unit 18, that is, on the mostdownstream side of the beamline BL. The substratetransferring/processing unit 20 includes an implantation processingchamber 40, a beam monitor 41, a beam profiler 42, a profiler drivingdevice 43, a substrate transfer device 44, and a load port 46. Theimplantation processing chamber 40 is provided with a platen drivingdevice (not illustrated) that holds the wafer W during the ionimplantation and moves the wafer W in a direction (y-direction)perpendicular to the beam scanning direction (x-direction).

The beam monitor 41 is provided on the most downstream side of thebeamline BL inside the implantation processing chamber 40. The beammonitor 41 is provided at a position into which the ion beam can beincident when the wafer W does not exist on the beamline BL, and isconfigured to measure the beam characteristics before or between the ionimplantation processes. The beam monitor 41 measures the beam current,the beam parallelism, or the like as the beam characteristic. Forexample, the beam monitor 41 is located close to a transfer port (notillustrated) connecting the implantation processing chamber 40 and thesubstrate transfer t device 44, and is provided at a position verticallybelow the transfer port.

The beam profiler 42 is configured to measure the beam current at aposition on the surface of the wafer W. The beam profiler 42 isconfigured to be movable in the x-direction by an operation of theprofiler driving device 43, is retreated from an implantation positionwhere the wafer W is located during the ion implantation, and isinserted into the implantation position when the wafer W is not locatedat the implantation position. The beam profiler 42 measures the beamcurrent while moving in the x-direction. In this manner, the beamprofiler 42 can measure the beam current over the entire beam scanningrange in the x-direction. In the beam profiler 42, a plurality ofFaraday cups may be aligned in an array in the x-direction so that thebeam currents can simultaneously be measured at a plurality of positionsin the beam scanning direction (x-direction).

The beam profiler 42 may include a single Faraday cup for measuring thebeam current, or may include an angle measurement device for measuringangle information of the beam. For example, the angle measurement deviceincludes a slit and a plurality of current detectors provided away fromthe slit in the beam traveling direction (z-direction). For example, theangle measurement device can measure angle components of the beam in theslit width direction by causing the plurality of current detectorsaligned in the slit width direction to measure the beam having passedthrough the slit. The beam profiler 42 may include a first anglemeasurement device capable of measuring the angle information in thex-direction and a second angle measurement device capable of measuringthe angle information in the y-direction.

The substrate transfer device 44 is configured to transfer the wafer Wbetween the load port 46 on which a wafer container 45 is placed and theimplantation processing chamber 40. The load port 46 is configured sothat a plurality of the wafer containers 45 can be placed at the sametime, and for example, has four placement tables aligned in thex-direction. A wafer container transfer port (not illustrated) isprovided vertically above the load port 46, and is configured so thatthe wafer container 45 can pass through the wafer container transferport in the vertical direction. For example, the wafer container 45 isautomatically loaded onto the load port 46 through the wafer containertransfer port by a transfer robot installed on a ceiling in asemiconductor manufacturing factory where the ion implanter 100 isinstalled, and is automatically unloaded from the load port 46.

The ion implanter 100 further includes a central control device 50. Thecentral control device 50 controls an overall operation of the ionimplanter 100. The central control device 50 is realized by an elementor a machine device such as a computer CPU or a memory in terms ofhardware, and is realized by a computer program or the like in terms ofsoftware. Various functions provided by the central control device 50can be realized in cooperation between the hardware and the software.

An operation panel 49 having a display unit and an input device forsetting operation parameters of the ion implanter 100 is provided in thevicinity of the central control device 50. The positions of theoperation panel 49 and the central control device 50 are notparticularly limited. For example, the operation panel 49 and thecentral control device 50 can be disposed adjacent to an entrance/exit48 of the maintenance area MA between the beam generation unit 12 andthe substrate transferring/processing unit 20. Work efficiency can beimproved by adjoining locations of the ion source 10, the load port 46,the operation panel 49, and the central control device 50 which arefrequently operated by an operator who manages the ion implanter 100.

Subsequently, a configuration of the beam acceleration unit 14 will bedescribed in detail. FIGS. 2A to 2C are sectional views illustratingeach configuration of the linear acceleration units 22 a to 22 c. FIG.2A illustrates a configuration of the first linear acceleration unit 22a, FIG. 2B illustrates a configuration of the second linear accelerationunit 22 b, and FIG. 2C illustrates a configuration of the third linearacceleration unit 22 c. The linear acceleration units 22 a to 22 cinclude high frequency accelerators 101 to 115 respectively in aplurality of stages disposed along the beamline BL and electrostaticquadrupole lens devices 121 to 139 respectively in a plurality of stagesdisposed along the beamline BL. At least one electrostatic quadrupolelens device is disposed in each of the upstream side and the downstreamside of the high frequency accelerators 101 to 115 respectively in theplurality of stages.

The high frequency accelerator accelerates or decelerates the ionparticles forming the ion beam IB by applying a high frequency voltageV_(RF) to a high frequency electrode through which the ion beam IBpasses. The high frequency accelerator in each of the stages isconfigured so that a voltage amplitude V₀, a frequency f, and a phase φof the high frequency voltage V_(RF) can individually be adjusted. Inthe present specification, the voltage amplitude V₀, the frequency f,and the phase φ of the high frequency voltage V_(RF) are collectivelyreferred to as “high frequency parameters”.

The electrostatic quadrupole lens device includes lens electrodes forcausing an electrostatic field to act on the ion beam IB to focus ordefocus the ion beam IB, and ground electrodes provided on the upstreamside and the downstream side of the lens electrodes. The electrostaticquadrupole lens device functions as a horizontally focusing (verticallydefocus) lens that causes the beam to converge in the x-direction, or avertically focusing (horizontally defocusing) lens that causes the beamto converge in the y-direction by switching positive and negativevoltages applied to the lens electrodes.

In FIGS. 2A to 2C, the lens electrodes facing in the y-direction areillustrated, and the lens electrodes facing in the x-direction areomitted. When the negative voltage is applied to the lens electrodesfacing in the y-direction, the electrostatic quadrupole lens devicefunctions as the horizontally focusing (vertically defocusing) lens. Onthe other hand, when the positive voltage is applied to the lenselectrodes facing in the y-direction, the electrostatic quadrupole lensdevice functions as the vertically focusing (horizontally defocusing)lens. Configurations of the lens electrodes will be described later withreference to FIGS. 3A and 3B.

The first linear acceleration unit 22 a includes high frequencyaccelerators 101, 102, 103, 104, and 105 in five stages andelectrostatic quadrupole lens devices 121, 122, 123, 124, 125, 126, and127 in seven stages. The electrostatic quadrupole lens devices 121 and122 in the first stage and the second stage are continuously disposed inan inlet of the first linear acceleration unit 22 a. Each of theelectrostatic quadrupole lens devices 123 to 127 from the third stage tothe seventh stage excluding the first stage and the second stage isdisposed on the downstream side of each of the high frequencyaccelerators 101 to 105 from the first stage to the fifth stage.

The electrostatic quadrupole lens devices 121 to 127 in seven stagesprovided in the first linear acceleration unit 22 a are disposed so thatthe horizontally focusing lens and the vertically focusing convergencelens are alternately disposed along the beamline BL. For example, theelectrostatic quadrupole lens devices 121, 123, 125, and 127 in thefirst stage, the third stage, the fifth stage, and the seventh stage arethe vertically focusing lenses, and the electrostatic quadrupole lensdevices 122, 124, and 126 in the second stage, the fourth stage, and thesixth stage are the horizontally focusing lenses.

The second linear acceleration unit 22 b includes high frequencyaccelerators 106, 107, 108, 109, and 110 in five stages andelectrostatic quadrupole lens devices 128, 129, 130, 131, 132, and 133in six stages. Each of the electrostatic quadrupole lens devices 129 to133 from the ninth stage to the thirteenth stage excluding theelectrostatic quadrupole lens device 128 in the eighth stage provided inan inlet of the second linear acceleration unit 22 b is disposed on thedownstream side of each of the high frequency accelerators 106 to 110from the sixth stage to the tenth stage. The electrostatic quadrupolelens devices 128 to 133 in six stages provided in the second linearacceleration unit 22 b are disposed so that the horizontally focusinglens and the vertically focusing lens are alternately disposed along thebeamline BL. For example, the electrostatic quadrupole lens devices 128,130, and 132 in the eighth stage, the tenth stage, and the twelfthstages are the horizontally focusing lenses, and the electrostaticquadrupole lens devices 129, 131, and 133 in the ninth stage, theeleventh stage, and the thirteenth stage are the vertically focusinglenses.

The third linear acceleration unit 22 c includes high frequencyaccelerators 111, 112, 113, 114, and 115 in five stages andelectrostatic quadrupole lens devices 134, 135, 136, 137, 138, and 139in six stages. Each of the electrostatic quadrupole lens devices 135 to139 from the fifteenth stage to the nineteenth stage excluding theelectrostatic quadrupole lens device 134 in the fourteenth stageprovided in an inlet of the third linear acceleration unit 22 c isdisposed on the downstream side of each of the high frequencyaccelerators 111 to 115 from the eleventh stage to the fifteenth stage.The electrostatic quadrupole lens devices 134 to 139 in six stagesprovided in the third linear acceleration unit 22 c are disposed so thatthe horizontally focusing lens and the vertically focusing lens arealternately disposed along the beamline BL. For example, theelectrostatic quadrupole lens devices 134, 136, and 138 in thefourteenth stage, the sixteenth stage, and the eighteenth stage are thehorizontally focusing lenses, and the electrostatic quadrupole lensdevices 135, 137, and 139 in the fifteenth stage, the seventeenth stage,and the nineteenth stage are the vertically focusing lenses.

The number of stages of the high frequency accelerators and theelectrostatic quadrupole lens devices which are included in the linearacceleration units 22 a to 22 c is not limited to that in theillustrated example, and a configuration may be adopted to have thenumber of stages different from that in the illustrated example. Inaddition, the disposition of the electrostatic quadrupole lens devicesmay be different from that in the illustrated example. For example, theelectrostatic quadrupole lens device in at least one stage may have onepair of the horizontally focusing lens and the vertically focusing lens,or may have a plurality of pairs of the horizontally focusing lens andthe vertically focusing lens.

FIGS. 3A and 3B are front views illustrating schematic configurations ofthe electrostatic quadrupole lens devices 52 a and 52 b when viewed fromthe upstream side of the beamline. The electrostatic quadrupole lensdevice 52 a in FIG. 3A is the horizontally focusing lens that causes theion beam IB to converge in a horizontal direction (x-direction), and theelectrostatic quadrupole lens device 52 b in FIG. 3B is the verticallyfocusing lens that causes the ion beam IB to converge in a verticaldirection (y-direction).

The electrostatic quadrupole lens device 52 a in FIG. 3A has a pair ofupper and lower lens electrodes 54 a facing in the vertical direction(y-direction) and a pair of left and right lens electrodes 56 a facingin the horizontal direction (x-direction). A negative potential −Qa isapplied to the upper and lower lens electrodes 54 a, and a positivepotential +Qa is applied to the left and right lens electrodes 56 a.With respect to the ion beam IB formed of positively charged ionparticles, the electrostatic quadrupole lens device 52 a generates anattractive force between the upper and lower lens electrodes 54 a havingthe negative potential, and generates a repulsive force between the leftand right lens electrodes 56 a having the positive potential. In thismanner, the electrostatic quadrupole lens device 52 a causes the ionbeam IB to converge in the x-direction and to diverge in the y-directionand adjusts a beam shape.

As in FIG. 3A, the electrostatic quadrupole lens device 52 b in FIG. 3Bhas a pair of upper and lower lens electrodes 54 b facing in thevertical direction (y-direction) and a pair of left and right lenselectrodes 56 b facing in the horizontal direction (x-direction). InFIG. 3B, applied positive and negative potentials are opposite to thosein FIG. 3A, a positive potential +Qb is applied to the upper and lowerlens electrodes 54 b, and a negative potential −Qb is applied to theleft and right lens electrodes 56 b. As a result, the electrostaticquadrupole lens device 52 b causes the ion beam IB to converge in they-direction and to diverge in the x-direction and adjusts the beamshape.

FIG. 4 is a sectional view illustrating a schematic configuration of thehigh frequency accelerator 70, and illustrates a configuration of thehigh frequency accelerator corresponding to one stage included in eachof the linear acceleration units 22 a to 22 c. The high frequencyaccelerator 70 includes a high frequency electrode 72, a high frequencyresonator 74, a stem 76, and a high frequency power supply 78. The highfrequency electrode 72 has a hollow cylindrical electrode body, and theion beam IB passes through the inside of the electrode body. The highfrequency electrode 72 is connected to the high frequency resonator 74via the stem 76. The high frequency power supply 78 supplies the highfrequency voltage V_(RF) to the high frequency resonator 74. The centralcontrol device 50 controls the high frequency resonator 74 and the highfrequency power supply 78 to adjust the voltage amplitude V₀, thefrequency f, and the phase φ of the high frequency voltage V_(RF)applied to the high frequency electrode 72.

The electrostatic quadrupole lens devices 52 a and 52 b are provided onthe upstream side and the downstream side of the high frequencyaccelerator 70. The electrostatic quadrupole lens device 52 a on theupstream side has a first ground electrode 60 a, a second groundelectrode 62 a, upper and lower lens electrodes 54 a, left and rightlens electrodes 56 a, and a lens power supply 58 a (refer to FIG. 3).The upper and lower lens electrodes 54 a and the left and right lenselectrodes 56 a are provided between the first ground electrode 60 a andthe second ground electrode 62 a. The electrostatic quadrupole lensdevice 52 b on the downstream side has a first ground electrode 60 b, asecond ground electrode 62 b, upper and lower lens electrodes 54 b, leftand right lens electrodes 56 b, and a lens power supply 58 b (refer toFIG. 3). The upper and lower lens electrodes 54 b and the left and rightlens electrodes 56 b are provided between the first ground electrode 60b and the second ground electrode 62 b.

In an example in FIG. 4, the electrostatic quadrupole lens device 52 aon the upstream side is the horizontally focusing (verticallydefocusing) lens, and the electrostatic quadrupole lens device 52 b onthe downstream side is the vertically focusing (horizontally defocusing)lens. The electrostatic quadrupole lens device 52 a on the upstream sidemay be the vertically focusing (horizontally defocusing) lens, and theelectrostatic quadrupole lens device 52 b on the downstream side may bethe horizontally focusing (vertically defocusing) lens, depending onwhich shape the high frequency accelerator 70 is located in. Thehorizontally focusing and the vertically focusing can be changed byinverting the positive and negative voltages applied by the lens powersupplies 58 a and 58 b.

The high frequency accelerator 70 in FIG. 4 accelerates or deceleratesion particle 68 forming the ion beam IB by using potential differencesin an upstream side gap 64 between the second ground electrode 62 a andthe high frequency electrode 72 on the upstream side, and in adownstream side gap 66 between the high frequency electrode 72 and thefirst ground electrode 60 b on the downstream side. For example, the ionparticle 68 passing through the high frequency accelerator 70 can beaccelerated by adjusting the phase φ of the high frequency voltageV_(RF) so that the negative voltage is applied to the high frequencyelectrode 72 when the ion particle 68 passes through the upstream sidegap 64, and the positive voltage is applied to the high frequencyelectrode 72 when the ion particle 68 passes through the downstream sidegap 66. The inside of the high frequency electrode 72 is substantiallyequipotential. Accordingly, the ion particle 68 is not accelerated ordecelerated when passing through the inside of the high frequencyelectrode 72.

FIG. 5 is a sectional view illustrating a detailed configuration of thelinear acceleration unit. FIG. 5 illustrates a configuration of thebeamline upstream side of the first linear acceleration unit 22 aillustrated in FIG. 2A, and illustrates the electrostatic quadrupolelens devices 121 to 125 from the first stage to the fifth stage and thehigh frequency accelerators 101 to 103 from the first stage to the thirdstage.

The first linear acceleration unit 22 a includes a vacuum chamber 140.The vacuum chamber 140 extends in the z-direction along the beamline BL.The vacuum chamber 140 has a rectangular cross section perpendicular tothe beamline BL, and has four partition walls extending in thez-direction. As the four partition walls, the vacuum chamber 140 has anupper wall 140 a, a left side wall 140 b, a right side wall 140 c (referto FIG. 6 to be described later), and a lower wall 140 d.

FIG. 6 is a sectional view illustrating the disposition of the vacuumchamber 140, and illustrates a cross section perpendicular to thez-axis. FIG. 5 corresponds to a cross section taken along a line A-A inFIG. 6. As illustrated in FIG. 6, the vacuum chamber 140 is disposed ina state rotated around the z-axis by 45 degrees. The upper wall 140 a isnot disposed on a vertically upper side (+y-direction) and is disposedon an upper left side (+v-direction) when viewed from the beamline BL.The +v-direction corresponds to a direction of a vector obtained bycombining unit vectors in the +x-direction and the +y-direction. Theleft side wall 140 b is disposed on a lower left side (+u-direction)when viewed from the beamline BL. The +u-direction corresponds to adirection of a vector obtained by combining unit vectors in the+x-direction and the −y-direction. The right side wall 140 c is disposedon an upper right side (−u-direction) when viewed from the beamline BL.The lower wall 140 d is disposed on a lower right side (−v-direction)when viewed from the beamline BL.

FIG. 6 further illustrates the disposition of high frequency resonators74 a to 74 c included respectively in the high frequency accelerators101 to 103. The first high frequency resonator 74 a included in the highfrequency accelerator 101 in the first stage is provided outside theupper wall 140 a, and is disposed at a position in the +v-direction whenviewed from the beamline BL. The first high frequency resonator 74 a isconnected to a first high frequency electrode 72 a via a first stem 76 aextending in the +v-direction when viewed from the beamline BL.

The second high frequency resonator 74 b included in the high frequencyaccelerator 102 in the second stage is provided outside the left sidewall 140 b, and is disposed at a position in the +u-direction whenviewed from the beamline BL. The second high frequency resonator 74 b isconnected to a second high frequency electrode 72 b (refer to FIG. 5)via a second stem 76 b extending in the +u-direction when viewed fromthe beamline BL.

The third high frequency resonator 74 c included in the high frequencyaccelerator 103 in the third stage is provided outside the right sidewall 140 c, and is disposed at a position in the −u-direction whenviewed from the beamline BL. The third high frequency resonator 74 c isconnected to a third high frequency electrode 72 c (refer to FIG. 5) viaa third stem 76 c extending in the −u-direction when viewed from thebeamline BL.

A high frequency resonator is not provided outside the lower wall 140 d.The lower wall 140 d is provided with a vacuum pump 148 for evacuatingthe inside of the vacuum chamber 140. The vacuum pump 148 is disposed ata position in the −v-direction when viewed from the beamline BL.

As illustrated in FIG. 6, the vacuum chamber 140 is disposed by beingrotated from a horizon by 45 degrees. In this manner, a range occupiedby the high frequency resonators 74 a to 74 c in the x-direction and they-direction can be reduced, and an overall size of the first linearacceleration unit 22 a can be reduced.

In the present specification, a direction in which the beamline BLextends may be referred to as an axial direction. In addition, adirection perpendicular to the axial direction may be referred to as aradial direction, and a direction perpendicular to both the axialdirection and the radial direction may be referred to as acircumferential direction. The x-axis, the y-axis, the u-axis, and thev-axis are respectively axes extending in the radial directions in whichangles in the circumferential direction are different from each other.

Referring back to FIG. 5, configurations of the high frequencyaccelerators 101 to 103 will be described. The high frequencyaccelerator 101 in the first stage includes a first high frequencyelectrode 72 a, a first high frequency resonator 74 a, a first stem 76a, and a first insulator 77 a. The first stem 76 a is inserted into amounting hole 146 provided on the upper wall 140 a. The first insulator77 a is provided outside the vacuum chamber 140 and inside the highfrequency resonator 74 a. The first insulator 77 a is mounted on theupper wall 140 a, and supports the first stem 76 a. The first insulator77 a is formed in a cone shape, and is provided to cover the mountinghole 146. The first insulator 77 a maintains electrical insulationbetween the vacuum chamber 140 which is the ground potential, and thefirst stem 76 a to which the high frequency voltage V_(RF) is applied.The first insulator 77 a is provided at a position in the +v-directionwhen viewed from the beamline BL.

The high frequency accelerator 102 in the second stage includes a secondhigh frequency electrode 72 b, a second high frequency resonator 74 b, asecond stem 76 b, and a second insulator (not illustrated). The highfrequency accelerator 102 in the second stage is configured in the samemanner as the high frequency accelerator 101 in the first stage. Amounting state is different as illustrated in FIG. 6. Specifically, thesecond stem 76 b is disposed at a position in the +u-direction whenviewed from the beamline BL. The second insulator is mounted on the leftside wall 140 b, and supports the second stem 76 b. The second insulatoris disposed at a position in the +u-direction when viewed from thebeamline BL.

The high frequency accelerator 103 in the third stage includes a thirdhigh frequency electrode 72 c, a third high frequency resonator 74 c, athird stem 76 c, and a third insulator (not illustrated). The highfrequency accelerator 103 in the third stage is configured in the samemanner as the high frequency accelerator 101 in the first stage. Themounting state is different as illustrated in FIG. 6. Specifically, thethird stem 76 c is disposed at a position in the −u-direction whenviewed from the beamline BL. The third insulator is mounted on the rightside wall 140 c, and supports the third stem 76 c. The third insulatoris disposed at a position in the −u-direction when viewed from thebeamline BL.

The plurality of electrostatic quadrupole lens devices 121 to 125 areprovided inside the vacuum chamber 140. Each of the plurality ofelectrostatic quadrupole lens devices 121 to 125 is configured to serveas a lens unit 80. The lens unit 80 is a unit which includes theelectrostatic quadrupole lens device 52 a (or 52 b) illustrated in FIGS.3(a), 3(b), and 4. The upper and lower lens electrodes 54 a (or 54 b),the left and right lens electrodes 56 a (or 56 b), the first groundelectrode 60 a (or 60 b), and the second ground electrode 62 a (or 62 b)are integrated with each other. In the present specification, the lensunit 80 is also referred to as the electrostatic quadrupole lens device.

The lens unit 80 includes a plurality of lens electrodes 82, an upstreamside cover electrode 84 a, a downstream side cover electrode 84 b, abase plate 86, and a mounting portion 88.

The plurality of lens electrodes 82 correspond to the upper and lowerlens electrodes 54 a (or 54 b) and the left and right lens electrodes 56a (or 56 b) which are illustrated in FIGS. 3A and 3B. The plurality oflens electrodes 82 face each other in the radial direction while thebeamline BL is interposed therebetween, and are disposed at an intervalin the circumferential direction. Specifically, a pair of the upper andlower lens electrodes face each other in the y-direction, and a pair ofthe left and right lens electrodes face each other in the x-direction.In addition, the two upper and lower lens electrodes and the two leftand right lens electrodes are alternately disposed in thecircumferential direction. A positive or negative focusing/defocusingvoltage is applied to each of the plurality of lens electrodes 82.

The upstream side cover electrode 84 a covers the beamline upstream sideof the plurality of lens electrodes 82. The upstream side coverelectrode 84 a is formed in a bowl shape configured to include only acurved surface or a curved surface and a flat surface. A beam incidentport through which the ion beam IB passes is provided in a center of theupstream side cover electrode 84 a. The upstream side cover electrode 84a is disposed away from the plurality of lens electrodes 82 in the axialdirection or in the radial direction. The upstream side cover electrode84 a is the ground electrode, and corresponds to the first groundelectrode 60 a (or 60 b) in FIG. 4.

The downstream side cover electrode 84 b covers the beamline downstreamside of the plurality of lens electrodes 82. As in the upstream sidecover electrode 84 a, the downstream side cover electrode 84 b isconfigured to include only a curved surface, or is formed in a bowlshape configured to include a curved surface and a flat surface. A beamexiting port through which the ion beam IB passes is provided in acenter of the downstream side cover electrode 84 b. The downstream sidecover electrode 84 b is disposed away from the plurality of lenselectrodes 82 in the axial direction or in the radial direction. Thedownstream side cover electrode 84 b is the ground electrode, andcorresponds to the second ground electrode 62 a (or 62 b) in FIG. 4.

The base plate 86 supports the plurality of lens electrodes 82, theupstream side cover electrode 84 a, and the downstream side coverelectrode 84 b. The base plate 86 is a plate-shaped member having athickness in the axial direction. The plurality of lens electrodes 82are accommodated in a central opening that penetrates a center of thebase plate 86. The upstream side cover electrode 84 a is mounted on theupstream side of the base plate 86. The downstream side cover electrode84 b is mounted on the downstream side of the base plate 86.

The mounting portion 88 is a portion fixed to the vacuum chamber 140.The mounting portion 88 is provided in the lower portion of the baseplate 86, and extends from the base plate 86 in the axial direction. Amounting bar 142 extending in the axial direction is provided on aninner surface of the vacuum chamber 140. The mounting portion 88 isfixed to the mounting bar 142 by using a fastening member 144 such as ascrew or a bolt.

FIG. 7 is an external perspective view illustrating an example of thelens unit 80 when viewed from the upstream side. For example, the lensunit 80 in FIG. 7 is the electrostatic quadrupole lens device 122 in thesecond stage adjacent to the upstream side of the high frequencyaccelerator 101 in the first stage. The upstream side cover electrode 84a has a beam incident port 92 a through which the ion beam IB passes,and a plurality of gas exhaust ports (also referred to as upstream sidegas exhaust ports) 94 a, 95 a, and 96 a. The beam incident port 92 a isprovided in a center of the upstream side cover electrode 84 a, and isopen in the axial direction. The plurality of upstream side gas exhaustports 94 a to 96 a are provided on an outer peripheral portion of theupstream side cover electrode 84 a, and are open in the radialdirection. Each of the plurality of upstream side gas exhaust ports 94 ato 96 a is provided to exhaust gas from the inside to the outside of thelens unit 80.

The plurality of upstream side gas exhaust ports 94 a to 96 a arerespectively provided at different positions in the circumferentialdirection, and for example, are provided at positions different fromeach other by 90 degrees in the circumferential direction. For example,the first gas exhaust port 94 a is provided at a position in the+u-direction when viewed from the beamline BL. The second gas exhaustport 95 a is provided at a position in the −u-direction when viewed fromthe beamline BL. The third gas exhaust port 96 a is provided at aposition in the −v-direction when viewed from the beamline BL. In theillustrated example, the gas exhaust port is not provided at a positionin the +v-direction when viewed from the beamline BL. A fourth gasexhaust port may be provided at the position in the +v-direction whenviewed from the beamline BL.

Each of the plurality of upstream side gas exhaust ports 94 a to 96 a isformed as a slit extending in the circumferential direction. Forexample, each of the plurality of upstream side gas exhaust ports 94 ato 96 a is formed as a slit continuously extending over an angle rangeof approximately 10 degrees to 60 degrees. Each of the plurality ofupstream side gas exhaust ports 94 a to 96 a may not continuously beformed in the circumferential direction, or may intermittently be formedin the circumferential direction. For example, each of the plurality ofupstream side gas exhaust ports 94 a to 96 a may be formed as a mesh, ormay be formed as a small aperture array.

The mounting portions 88 are provided in both ends of the base plate 86in a rightward-leftward direction (u-direction), and are not providednear the center of the base plate 86 in the rightward-leftwarddirection. The mounting portion 88 is formed to have a cutout 88 aprovided on the upstream side. The cutout 88 a on the upstream side isprovided between the beamline BL and the vacuum pump 148. For example,the cutout 88 a on the upstream side allows the gas flowing toward thevacuum pump 148 from the plurality of upstream side gas exhaust ports 94a to 96 a to pass therethrough. The cutout 88 a on the upstream side maynot continuously be formed, or may be formed as a mesh or a smallaperture array.

FIG. 8 is an external perspective view illustrating the lens unit 80 inFIG. 7 when viewed from the downstream side. In the illustrated example,configurations on the upstream side and the downstream side of the lensunit 80 are the same as each other. The downstream side cover electrode84 b has a beam exiting port 92 b through which the ion beam IB passes,and a plurality of gas exhaust ports (also referred to as downstreamside gas exhaust ports) 94 b, 95 b, and 96 b. The beam exiting port 92 bis provided in a center of the downstream side cover electrode 84 b, andis open in the axial direction. The plurality of downstream side gasexhaust ports 94 b to 96 b are provided on an outer peripheral portionof the downstream side cover electrode 84 b, and are open in the radialdirection. For example, the plurality of downstream side gas exhaustports 94 b to 96 b are configured in the same manner as the plurality ofupstream side gas exhaust ports 94 a to 96 a provided in the upstreamside cover electrode 84 a. Each of the plurality of downstream side gasexhaust ports 94 b to 96 b is provided to exhaust the gas from theinside to the outside of the lens unit 80.

As in the upstream side, the mounting portion 88 has a cutout 88 bprovided on the downstream side. The cutout 88 b on the downstream sideis provided between the beamline BL and the vacuum pump 148. Forexample, the cutout 88 b on the downstream side allows the gas flowingtoward the vacuum pump 148 from the plurality of downstream side gasexhaust ports 94 b to 96 b to pass therethrough. The cutout 88 b on thedownstream side may not continuously be formed, or may be formed as amesh or a small aperture array.

FIG. 9 is a sectional view taken along the beamline BL, whichillustrates a detailed internal configuration of the lens unit 80 inFIG. 7, and is an enlarged view of the lens unit 80 illustrated in FIG.5. For example, the lens unit 80 in FIG. 9 is the electrostaticquadrupole lens device 122 in the second stage adjacent to the upstreamside of the high frequency accelerator 101 in the first stage. The lensunit 80 includes a plurality of insulating members 90 that respectivelysupport the plurality of lens electrodes 82. For example, the pluralityof insulating members 90 are columnar insulators. Each of the pluralityof insulating members 90 extends outward in the radial direction fromthe corresponding lens electrode 82 toward the base plate 86. Each ofthe plurality of insulating members 90 is mounted on an inner peripheralsurface 86 b of a central opening 86 a of the base plate 86. A wiringport 86 c extending in the v-direction is provided in the lower portionof the base plate 86. Wires (not illustrated) for applying high voltagesto the plurality of lens electrodes 82 are inserted through the wiringport 86 c.

The plurality of gas exhaust ports 94 a to 96 a and 94 b to 96 bprovided in the upstream side cover electrode 84 a and the downstreamside cover electrode 84 b are provided at positions farther away fromthe beamline BL in the radial direction than the plurality of lenselectrodes 82. That is, the plurality of gas exhaust ports 94 a to 96 aand 94 b to 96 b are provided on rear sides of the plurality of lenselectrodes 82 when viewed from the beamline BL. Since the plurality ofgas exhaust ports 94 a to 96 a and 94 b to 96 b are provided on the rearsides of the plurality of lens electrodes 82, it is possible to adopt aconfiguration in which spatial distribution of a focusing/defocusingelectric field acting on the ion beam IB is substantially not changed.That is, it is possible to prevent a change in focusing/defocusingperformance of the lens unit 80 which is caused by the provided gasexhaust ports.

Positions of the plurality of gas exhaust ports 94 a to 96 a and 94 b to96 b in the axial direction are in ranges C1 and C2 between positions ofend portions 82 a and 82 b of the plurality of lens electrodes 82 in theaxial direction and positions of the plurality of insulating members 90in the axial direction. The plurality of upstream side gas exhaust ports94 a to 96 a are provided in the range C1 between the upstream side endportion 82 a of the plurality of lens electrodes 82 and the plurality ofinsulating members 90. That is, the plurality of upstream side gasexhaust ports 94 a to 96 a are provided to avoid positions on theupstream side of the upstream side end portion 82 a of the plurality oflens electrodes 82. In this manner, it is possible to prevent a changein the function of the upstream side cover electrode 84 a serving as theground electrode which is caused by the provided gas exhaust ports. Inaddition, the plurality of downstream side gas exhaust ports 94 b to 96b are provided in the range C2 between the downstream side end portion82 b of the plurality of lens electrodes 82 and the plurality ofinsulating members 90. That is, the plurality of downstream side gasexhaust ports 94 b to 96 b are provided to avoid positions on thedownstream side of the downstream side end portion 82 b of the pluralityof lens electrodes 82. In this manner, it is possible to prevent achange in the function of the downstream side cover electrode 84 bserving as the ground electrode which is caused by the provided gasexhaust ports. In addition, since the plurality of gas exhaust ports 94a to 96 a and 94 b to 96 b are provided to avoid the positions of theplurality of insulating members 90 in the axial direction, a flow of thegas toward the plurality of insulating members 90 can be suppressed, anda possibility that sputter particles may adhere to the plurality ofinsulating members 90 can be suppressed.

FIG. 10 is a sectional view perpendicular to the beamline BL, whichillustrates a detailed internal configuration of the lens unit 80 inFIG. 7. FIG. 10 illustrates the lens unit 80 in a state where theupstream side cover electrode 84 a is removed when viewed from thebeamline upstream side. For example, the lens unit 80 in FIG. 10 is theelectrostatic quadrupole lens device 122 in the second stage adjacent tothe upstream side of the high frequency accelerator 101 in the firststage.

FIG. 10 illustrates a disposition relationship of the plurality of lenselectrodes 82 and the plurality of downstream side gas exhaust ports 94b to 96 b in the circumferential direction. As illustrated, each of theplurality of downstream side gas exhaust ports 94 b to 96 b is disposedto be shifted from the plurality of lens electrodes 82 in thecircumferential direction. For example, each of the plurality ofdownstream side gas exhaust ports 94 b to 96 b is shifted to bedisplaced by 45 degrees from each of the plurality of lens electrodes82. For example, when a direction in which the first stem 76 a extends(+v-direction) is 0 degrees, the plurality of lens electrodes 82 aredisposed at positions of 45 degrees, 135 degrees, 225 degrees, and 315degrees. The plurality of downstream side gas exhaust ports 94 b to 96 bare disposed at positions of 270 degrees, 90 degrees, and 180 degrees.The plurality of upstream side gas exhaust ports 94 a to 96 a (notillustrated in FIG. 10) are similarly disposed at positions of 270degrees, 90 degrees, and 180 degrees to correspond to the plurality ofdownstream side gas exhaust ports 94 b to 96 b.

In the lens unit 80, when the ion beam IB collides with the electrodebody of the lens electrode 82 or the cover electrode 84 a or 84 b, theelectrode body is sputtered, and the substance forming the electrodebody is scattered as the sputter particles. The generated sputterparticles may adhere to the surface of the electrode body or theinsulating member 90 as dirt. The sputter particles are a conductivesubstance. The sputter particles adhere to the surface of the electrodebody and form fine irregularities. AS a result, discharge is likely tooccur between the electrodes. For example, the discharge may occurbetween the lens electrode 82 to which the high voltage is applied andthe cover electrode 84 a or 84 b which is the ground potential. Inaddition, when the sputter particles adhere to the surface of theinsulating member 90, insulating performance of the insulating member 90is degraded. Consequently, there is a possibility that electricalinsulation may not be ensured between the lens electrode 82 to which thehigh voltage is applied and the base plate 86 which is the groundpotential.

According to the present embodiment, the lens unit 80 is provided withthe plurality of gas exhaust ports 94 a to 96 a and 94 b to 96 b.Therefore, it is possible to generate a flow of the gas outward from theinside of the lens unit 80 through the plurality of gas exhaust ports 94a to 96 a and 94 b to 96 b. For example, as illustrated in FIG. 10, itis possible to generate a flow F of the gas toward the vacuum pump 148provided in the lower portion (−v-direction) of the vacuum chamber 140through the plurality of downstream side gas exhaust ports 94 b to 96 b.At least a portion of the sputter particles generated inside the lensunit 80 is exhausted outward of the lens unit 80 along the flow F of thegas outward from the inside of the lens unit 80. As a result, it ispossible to suppress a possibility that the sputter particles may adhereto the electrode body or the insulating member 90 provided inside thelens unit 80, and it is possible to suppress the discharge occurringbetween the electrode bodies or degradation of the insulatingperformance of the insulating member 90.

In the lens unit 80 illustrated in FIG. 10, the gas exhaust port is notprovided at a position of 0 degrees where the adjacent first stem 76 aexists. The first stem 76 a is supported by the first insulator 77 a,and when the sputter particles adhere to the first insulator 77 a, theinsulating performance of the first insulator 77 a is degraded. Sincethe gas exhaust port is not provided at the position of 0 degrees wherethe adjacent first stem 76 a exists, it is possible to suppress apossibility that the sputter particles may be scattered toward the firstinsulator 77 a, and it is possible to suppress the degradation of theinsulating performance of the first insulator 77 a.

In order to suppress the possibility that the sputter particles may bescattered toward the first insulator 77 a, it is preferable to providethe plurality of downstream side gas exhaust ports 94 b to 96 b atpositions shifted from the first stem 76 a by 45 degrees or larger inthe circumferential direction. In particular, in the cover electrodeadjacent to the high frequency accelerator 101 in the first stage, it ispreferable that the gas exhaust port is not provided at the position inthe +v-direction when viewed from the beamline BL. The cover electrodesadjacent to the high frequency accelerator 101 in the first stage arethe downstream side cover electrode of the electrostatic quadrupole lensdevice 122 in the second stage and the upstream side cover electrode ofthe electrostatic quadrupole lens device 123 in the third stage.

In the high frequency accelerator 102 in the second stage, the secondstem 76 b exists at a position in the +u-direction when viewed from thebeamline BL (refer to FIG. 6). Therefore, in a case of the coverelectrode adjacent to the high frequency accelerator 102 in the secondstage, it is preferable that the gas exhaust port is not provided at theposition in the +u-direction when viewed from the beamline BL, and thatthe plurality of gas exhaust ports are provided at the positions in the+v-direction, the −v-direction, and the −u-direction. The coverelectrodes adjacent to the high frequency accelerator 102 in the secondstage are the downstream side cover electrode of the electrostaticquadrupole lens device 123 in the third stage and the upstream sidecover electrode of the electrostatic quadrupole lens device 124 in thefourth stage.

In addition, in the high frequency accelerator 103 in the third stage,the third stem 76 c exists at a position in the −u-direction when viewedfrom the beamline BL (refer to FIG. 6). Therefore, in a case of thecover electrode adjacent to the high frequency accelerator 103 in thethird stage, it is preferable that the gas exhaust port is not providedat the position in the −u-direction when viewed from the beamline BL,and that the plurality of gas exhaust ports are provided at thepositions in the +v-direction, the −v-direction, and the +u-direction.The cover electrodes adjacent to the high frequency accelerator 103 inthe third stage are the downstream side cover electrode of theelectrostatic quadrupole lens device 124 in the fourth stage and theupstream side cover electrode of the electrostatic quadrupole lensdevice 125 in the fifth stage.

In a case of the cover electrode which is not adjacent to the highfrequency accelerator, the gas exhaust ports may be provided in fourdirections of ±v-direction and ±u-direction. That is, the coverelectrode may have four gas exhaust ports provided at the positions of 0degrees, 90 degrees, 180 degrees, and 270 degrees. The cover electrodeswhich are not adjacent to the high frequency accelerator are theupstream side and downstream side cover electrodes of the electrostaticquadrupole lens device 121 in the first stage and the upstream sidecover electrode of the electrostatic quadrupole lens device 122 in thesecond stage.

According to the present embodiment, since the cutouts 88 a and 88 b areprovided in the mounting portion 88, conductance of the gas flowing pathtoward the vacuum pump 148 can be improved. In particular, residual gascan effectively be exhausted by providing the cutouts 88 a and 88 b atlocations where the lens units 80 in the plurality of stages arecontinuously provided. For example, the residual gas can effectively beexhausted from a space between the electrostatic quadrupole lens devices121 and 122 in the first stage and the second stage which arecontinuously adjacent to each other.

According to the present embodiment, the residual gas can effectively beexhausted from the inside of the lens unit 80 through the plurality ofgas exhaust ports 94 a to 96 a and 94 b to 96 b. Therefore, a degree ofvacuum inside the lens unit 80 can be improved. In addition, the degreeof vacuum can be improved by effectively exhausting the residual gasfrom a space around the lens unit 80 through the cutouts 88 a and 88 b.In this manner, the degree of vacuum in the beamline BL can be improvedin the whole vacuum chamber 140. In this manner, it is possible toreduce influence of an interaction between the ion beam IB and theresidual gas which may decrease the charge state of the ions forming theion beam IB or may neutralize the ions. In this manner, transportefficiency of the ion beam IB in the beam acceleration unit 14 can beimproved, and a decrease in the beam current of the ion beam IB outputfrom the beam acceleration unit 14 can be suppressed.

The present embodiment may be applied to an ultra-high energy multistagelinear acceleration unit that accelerates the ion beam IB to 4 MeV orhigher. In order to accelerate the ion beam IB to 4 MeV or higher, it isnecessary to further increase the acceleration voltages applied to thehigh frequency accelerators 101 to 115 in the plurality of stages, andit is necessary to further increase the focusing/defocusing voltagesapplied to the electrostatic quadrupole lens devices 121 to 139 in theplurality of stages. When the higher voltage is applied, the dischargeis likely to occur between the electrode bodies. According to thepresent embodiment, it is possible to suppress a possibility that theelectrode body or the insulating member may be contaminated by thesputter particles. Therefore, the discharge occurring between theelectrode bodies can be suppressed.

The present embodiment may be applied to a high energy multistage linearacceleration unit that accelerates the ion beam IB containing multiplycharged ions. The acceleration energy given to the ion beam IB in thehigh frequency accelerator is proportional to a product of theacceleration voltage applied to the high frequency accelerator and thecharge state of the ions. Accordingly, the ions having a high chargestate are used so that the acceleration energy can be increased comparedto a case of using the ions having a low charge state. On the otherhand, the ions having the high charge state (for example, the ionshaving a triple or higher charge state or quadruple or higher chargestate) are likely to interact with the residual gas existing in thebeamline BL, and the interaction lowers the charge state, therebycausing a loss in the beam transport. According to the presentembodiment, the degree of vacuum of the beamline BL can be improved.Therefore, the loss of the multiply charged ions can be suppressed, anda decrease in the beam current of the ion beam IB output from the beamacceleration unit 14 can be suppressed.

The lens unit 80 according to the present embodiment may be applied toall of the electrostatic quadrupole lens devices 121 to 139 in theplurality of stages provided in the beam acceleration unit 14. That is,the gas exhaust port may be provided in the cover electrode included ineach of the electrostatic quadrupole lens devices 121 to 139 in theplurality of stages. The lens unit 80 according to the presentembodiment may be applied to the electrostatic quadrupole lens devices121 to 139 in some stages out of the plurality of stages provided in thebeam acceleration unit 14. That is, the lens unit 80 may be applied toat least one of the electrostatic quadrupole lens devices 121 to 139 inthe plurality of stages.

The lens unit 80 according to the present embodiment may be applied tothe electrostatic quadrupole lens device in at least one stage from themost upstream stage to a predetermined stage of the beam accelerationunit 14. For example, the lens unit 80 may be applied to theelectrostatic quadrupole lens devices 121 to 125 in the first stage tothe fifth stage illustrated in FIG. 5. The sputter particles generatedin the lens unit 80 are likely to be generated when the energy of theion beam IB is relatively low. Accordingly, the sputter particles aremore likely to be generated in the upstream portion than in thedownstream portion of the beam acceleration unit 14. For example,compared to the second linear acceleration unit 22 b or the third linearacceleration unit 22 c, the sputter particles are more likely to begenerated in the first linear acceleration unit 22 a. Therefore, thelens unit 80 may be applied to the upstream portion of the beamacceleration unit 14 in which the sputter particles are likely to begenerated. In this manner, an advantageous effect of exhausting thesputter particles can easily be achieved. On the other hand, the gasexhaust port may not be provided in the cover electrode, in theelectrostatic quadrupole lens devices (for example, 126 to 139) in thedownstream portion of the beam acceleration unit 14 in which the sputterparticles are less likely to be generated.

Hitherto, the present invention has been described with reference to theabove-described respective embodiments. However, the present inventionis not limited to the above-described respective embodiments. Those inwhich configurations of the respective embodiments are appropriatelycombined or replaced with each other are also included in the presentinvention. Based on the knowledge of those skilled in the art, therespective embodiments can be combined with each other, the processingsequences can be appropriately rearranged, or various modifications suchas design changes can be added to the embodiment. The embodiment havingthe added modifications can also be included in the scope of the presentinvention.

In the above-described embodiment, a case has been described where theplurality of gas exhaust ports 94 a to 96 a and 94 b to 96 b areprovided in each of the upstream side cover electrode 84 a and thedownstream side cover electrode 84 b. In another embodiment, theplurality of gas exhaust ports may be provided in only one of theupstream side cover electrode 84 a and the downstream side coverelectrode 84 b.

In the above-described embodiment, a case has been described where theplurality of gas exhaust ports 94 a to 96 a and 94 b to 96 b areprovided in each of the upstream side cover electrode 84 a and thedownstream side cover electrode 84 b. In another embodiment, only onegas exhaust port may be provided in at least one of the upstream sidecover electrode 84 a and the downstream side cover electrode 84 b.Therefore, at least one of the upstream side cover electrode 84 a andthe downstream side cover electrode 84 b may have at least one gasexhaust port.

It should be understood that the invention is not limited to theabove-described embodiment, but may be modified into various forms onthe basis of the spirit of the invention. Additionally, themodifications are included in the scope of the invention.

What is claimed is:
 1. An ion implanter comprising: a high energymultistage linear acceleration unit for accelerating an ion beam,wherein the high energy multistage linear acceleration unit includeshigh frequency accelerators in a plurality of stages provided along abeamline through which the ion beam travels, and electrostaticquadrupole lens devices in a plurality of stages provided along thebeamline, the electrostatic quadrupole lens device in each of the stagesincludes a plurality of lens electrodes facing each other in a radialdirection perpendicular to an axial direction in which the beamlineextends while the beamline is interposed between the plurality of lenselectrodes facing each other, and disposed at an interval in acircumferential direction perpendicular to both the axial direction andthe radial direction, an upstream side cover electrode covering abeamline upstream side of the plurality of lens electrodes, andincluding a beam incident port opening in the axial direction, and adownstream side cover electrode covering a beamline downstream side ofthe plurality of lens electrodes, and including a beam exiting portopening in the axial direction, and at least one of the upstream sidecover electrode and the downstream side cover electrode which areincluded in the electrostatic quadrupole lens device in at least one ofthe plurality of stages includes at least one gas exhaust port openingin the radial direction.
 2. The ion implanter according to claim 1,wherein the at least one gas exhaust port is provided at a positionfarther away from the beamline in the radial direction than theplurality of lens electrodes.
 3. The ion implanter according to claim 1,wherein the at least one gas exhaust port is provided at a positionshifted in the circumferential direction from each of the plurality oflens electrodes.
 4. The ion implanter according to claim 3, wherein theat least one gas exhaust port is provided at a position shifted by 45degrees in the circumferential direction from at least one of theplurality of lens electrodes.
 5. The ion implanter according to claim 1,wherein the at least one gas exhaust port includes a plurality of gasexhaust ports provided at different positions in the circumferentialdirection.
 6. The ion implanter according to claim 1, wherein the atleast one gas exhaust port is formed as a slit extending in thecircumferential direction.
 7. The ion implanter according to claim 1,wherein the at least one gas exhaust port is formed as a mesh or a smallaperture array.
 8. The ion implanter according to claim 1, wherein theelectrostatic quadrupole lens device in each of the stages furtherincludes a plurality of insulating members respectively supporting theplurality of lens electrodes, and each of the plurality of insulatingmembers is provided to extend outward in the radial direction from thecorresponding lens electrode, and a position of the at least one gasexhaust port in the axial direction is located between positions of endportions of the plurality of lens electrodes in the axial direction andpositions of the plurality of insulating members in the axial direction.9. The ion implanter according to claim 1, wherein the high frequencyaccelerator in each of the stages includes a hollow cylindrical highfrequency electrode through which the ion beam passes, a stem extendingoutward in the radial direction from the high frequency electrode, ahigh frequency resonator connected to the high frequency electrode viathe stem, and an insulator supporting the stem, and the at least one gasexhaust port is provided at a position shifted in the circumferentialdirection from the stem extending from the high frequency electrodeadjacent to the cover electrode in the axial direction.
 10. The ionimplanter according to claim 9, wherein the at least one gas exhaustport is provided at a position shifted by 45 degrees or more in thecircumferential direction from the stem.
 11. The ion implanter accordingto claim 9, wherein the at least one gas exhaust port includes a firstgas exhaust port provided at a position shifted by 90 degrees in thecircumferential direction from the stem, a second gas exhaust portprovided at a position shifted by 180 degrees in the circumferentialdirection from the stem, and a third gas exhaust port provided at aposition shifted by 270 degrees in the circumferential direction fromthe stem.
 12. The ion implanter according to claim 1, wherein theelectrostatic quadrupole lens device in each of the stages furtherincludes a base plate supporting the plurality of lens electrodes andthe cover electrodes, and a mounting portion extending from the baseplate in the axial direction and fixed to a vacuum chamber of the highenergy multistage linear acceleration unit, and the mounting portionincluded in the electrostatic quadrupole lens device in the at least oneof the plurality of stages includes a cutout through which gas insidethe vacuum chamber passes.
 13. The ion implanter according to claim 12,wherein the cutout is provided between the beamline and a vacuum exhaustsystem connected to the vacuum chamber.
 14. The ion implanter accordingto claim 12, wherein the cutout is formed as a mesh or a small aperturearray.
 15. The ion implanter according to claim 12, wherein theelectrostatic quadrupole lens device including the cutout is disposedadjacent to another electrostatic quadrupole lens device in the axialdirection.
 16. The ion implanter according to claim 1, wherein theelectrostatic quadrupole lens device in the at least one of theplurality of stages is provided in at least one stage from an uppermoststage to a predetermined stage in the high energy multistage linearacceleration unit.
 17. The ion implanter according to claim 1, whereinthe high energy multistage linear acceleration unit accelerates the ionbeam including multiply charged ions.
 18. The ion implanter according toclaim 1, wherein the high energy multistage linear acceleration unitaccelerates the ion beam up to energy of 4 MeV or higher.
 19. The ionimplanter according to claim 1, wherein the high frequency acceleratorsin the plurality of stages are provided in 10 or more stages, and theelectrostatic quadrupole lens devices in the plurality of stages areprovided in 10 or more stages.
 20. An electrostatic quadrupole lensdevice comprising: a plurality of lens electrodes facing each other in aradial direction perpendicular to an axial direction in which a beamlineextends while the beamline is interposed between the plurality of lenselectrodes facing each other, and disposed at an interval in acircumferential direction perpendicular to both the axial direction andthe radial direction; an upstream side cover electrode covering abeamline upstream side of the plurality of lens electrodes, andincluding a beam incident port opening in the axial direction; and adownstream side cover electrode covering a beamline downstream side ofthe plurality of lens electrodes, and including a beam exiting portopening in the axial direction, wherein at least one of the upstreamside cover electrode and the downstream side cover electrode includes atleast one gas exhaust port opening in the radial direction.